1. Field of the Invention
This invention relates to a thin-film, perpendicular magnetic recording and reproducing head.
2. Description of the Prior Art
Thin-film, perpendicular magnetic recording and reproducing heads have a high frequency response, and due to advances in semiconductor technology, highly accurate heads of this type can be manufactured at a low cost. They are expected to be used more commonly than magnetic heads of any other type.
Thin-film, perpendicular magnetic recording and reproducing heads can be classified into inductive heads, which are used for recording and reproducing purposes, and magnetoresistive heads, which are used for reproducing purposes. For example, an inductive head comprises a magnetic substrate formed from, e.g., soft ferrite; an insulating layer located on the magnetic substrate, this insulating layer containing a thin-film conductor; a main pole provided on the insulating layer and formed from Permally, Sendust, or an amorphous alloy; and a protective overcoat covering the main pole. These thin-film, perpendicular magnetic recording and reproducing heads have hitherto been manufactured by a process which involves:
(a) Forming a plurality of appropriately located grooves in a principal surface of a magnetic material, filling the grooves with a nonmagnetic material, such as glass, SiO.sub.2, Al.sub.2 O.sub.3 or barium titanate, and then finely polishing the principal surface of the so-formed magnetic substrate: PA1 (b) Forming a thin-film conductor coil on the polished surface of the magnetic substrate and then forming an insulating layer on the conductor coil, the insulating layer consisting of either an organic material such as a resist or a polyimide, or an inorganic oxide such as SiO.sub.2, to provide electrical insulation between the conductor coil and a main pole, the insulating layer having a thickness of 3 to 8 .mu.m if it is formed from an organic resin, or 5 to 15 .mu.m if it is formed from an inorganic oxide; PA1 (c) Flattening the exposed surface of the insulating layer by the etchback method employing a resist, which is described, for example, in Technical Report U.S. 86-13 of The Institute of Electrical Communication Engineers of Japan, to remove its unevenness (it is uneven because of the presence of the conductor coil under the insulating layer); PA1 (d) Forming a via hole in the insulating layer so as to provide a magnetic contact between subsequently formed main pole and the magnetic substrate; and PA1 (e) Forming the main pole on the exposed surface of the insulating layer and the exposed surface portion of the magnetic substrate, then forming a magnetic film and a protective overcoat thereon, and then cutting the whole assembly to a predetermined size and polishing it.
However, when the insulating layer is formed of an organic resin, such as a photoresist, it has a number of drawbacks. For example, organic resin is so low in heat resistance that it is likely to be decomposed during a heat treatment process. In addition, the insulating layer is likely to be separated from the main pole or the substrate during a heat treatment process because of its higher coefficient of thermal expansion. For example, the insulating layer is decomposed at a temperature of 500.degree. C. during the heat treatment process so that it is separated from the main pole. Also, its low thermal conductivity interferes with the smooth dissipation of the heat which is generated when an electric current is fed to the conductor coil so that a satisfactorily high input current can not be used. Moreover, if an organic resin is exposed in the surface of the head facing a magnetic recording medium, it presents a serious problem such as a head crash.
These problems can be solved if the insulating layer is formed from an inorganic oxide. The layer is, however, required to have a thickness of 5 to 15 .mu.m. This thickness is so large that it takes an undesirably long time to form the via hole therein.
Another problem with the conventional process is that a sharp edge is formed in the surface the insulating layer adjacent the via hole. As such, that portion of the main pole which overlies this sharp edge of the insulating layer will have a reduced and nonuniform thickness, which will lower its magnetic properties. The magnetic properties of the main pole, particularly, of the main pole having a thickness of less than 1 .mu.m, usually depend on the nature of the surface of the insulating layer and the substrate, such as roughness and residual stress. In this connection, the conventional process is not satisfactory. In particular, the etchback method is not effective for flattening the surface of the insulating layer and improving the roughness of the surface of the insulating layer, i.e., it is an inefficient method which requires a great deal of time and labor.